A digital signature binds a message to a key pair: produce a signature with the private key, anyone verifies with the public key, and forgery should be computationally infeasible. On blockchains the ‘message’ is usually a structured transaction: nonce, gas limits, recipient, calldata — encoded canonically so validators recompute the same digest before checking the signature. Ethereum EOAs use ECDSA on secp256k1; Bitcoin script paths wrap CHECKSIG operations around comparable math.
What happens under the verification hood